Polytetrafluoroethylene tube

ABSTRACT

A polytetrafluoroethylene tube is provided and has a thickness of 0.1 mm or less, a tensile elongation at break of 350% or more, and a melting energy of 0.6 J/g or more which is calculated from an endothermic peak at 370° C.±5° C. in a procedure of increasing a temperature in differential scanning calorimetry (DSC).

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of International Application No.PCT/JP2017/009559 filed on Mar. 9, 2017, which is based on and claimspriority from Japanese Patent Application Nos. 2016-056365, 2016-066946,2016-172416, and 2017-041101, filed on Mar. 20, 2016. Mar. 29, 2016,Sep. 5, 2016, and Mar. 3, 2017, respectively, the entire contents ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to a fluororesin tube, and particularly,to a tube of polytetrafluoroethylene (referred to as “PTFE” below) as amaterial of the tube, having a thin thickness.

Background Art

A PTFE tube is suitably used in a material and the like of a medicalcatheter because of excellent characteristics such as chemicalresistance, non-adhesiveness, and low friction. In an endovascularsurgery, a catheter is inserted into a blood vessel and a lesion site ina blood vessel is removed, treated, or the like. Because a burden of apatient is small, such an endovascular surgery becomes the mainstream.It is necessary that a catheter used for such a purpose ispercutaneously inserted toward the inside of a body, and a tip end ofthe tube is caused to reach a lesion site via a blood vessel. Inaddition, the catheter requires, for example, straightness whichrepresents straightly traveling in a blood vessel and operationtransmissibility which represents transmission of an operation of apractitioner who performs treatment. In order to satisfy the demand, thecatheter is configured by stacking layers which have differentcharacteristics. The inner diameter of the catheter is preferably aslarge as possible, because it is necessary that, for example, a jig isinserted or a chemical liquid is injected into the catheter. Inaddition, the outer diameter of the catheter is preferably small inorder to reduce the burden on a patient. Thus, each of the layersconstituting the catheter is required to be as thin as possible.

As one method of manufacturing a catheter tube, there is a method inwhich a core wire such as a copper wire is coated with PTFE, an exteriorresin layer is formed on the resultant of the coating, then the corewire is pulled out, and thereby a catheter tube is obtained (forexample, see Patent Document 1). As a method of coating a core wire withPTFE, there are a method (referred to as “a dipping method” below) ofcoating a core wire with a PTFE dispersion and sintering the resultantof the coating, and a method of performing direct paste extrusionforming on the core wire. In addition, there is a method of performingcoating by covering a core wire with a PTFE tube. At this time, the PTFEtube is extended in a state where the core wire is inserted into thePTFE tube, the diameter thereof is reduced, and thus the PTFE tubeadheres to the core wire. Thus, the tube requires an elongation forperforming extension and a tensile strength for withstanding extension.

Since PTFE has a very large melt viscosity, a PTFE tube is generallyformed by not melt extrusion forming but paste extrusion forming (forexample, see Patent Document 2). However, in the paste extrusionforming, it is difficult to form a tube having a thin thickness. In acase of forming a PTFE tube having a thin thickness, the dipping methodis much used (for example, see Patent Document 3). However, a tubeformed by the dipping method has a problem of weak tensile strength.

For example, Patent Document 4 discloses a method in which the pasteextrusion forming is performed, and then the tube is extended in alongitudinal direction so as to reduce the thickness, in order to obtaina tube which has a thin thickness and a large tensile strength.

CITATION LIST

-   Patent Document 1: JP-A-2013-176583-   Patent Document 2: JP-A-2010-226936-   Patent Document 3: JP-A-2000-316977-   Patent Document 4: JP-A-2004-340364

SUMMARY

In the technique disclosed in Patent Document 4, since extension isperformed for reducing the thickness, the tensile strength of a PTFEtube is large, but the tensile elongation is reduced. As describedabove, it is difficult that a PTFE tube having a thin thickness obtainsboth the tensile elongation and the tensile strength. Accordingly, anobject of the present invention is to provide a PTFE tube which is athin PTFE tube and has a large tensile strength, while having a largetensile elongation at break.

The object of the present invention is achieved by apolytetrafluoroethylene tube having a thickness of 0.1 mm or less, atensile elongation at break of 350% or more, and a melting energy of 0.6J/g or more which is calculated from an endothermic peak at 370° C.±5°C. in a procedure of increasing a temperature in differential scanningcalorimetry (DSC).

The object of the present invention is achieved by apolytetrafluoroethylene tube having a thickness of 0.1 mm or less, atensile elongation at break of 450% or more, and a melting energy of 0.6J/g or more which is calculated from an endothermic peak at 370° C.+±5°C. in a procedure of increasing a temperature in differential scanningcalorimetry (DSC).

Further, the object of the present invention is achieved by apolytetrafluoroethylene tube in which a tensile strength at a tubedisplacement amount of 10 mm when being measured at a distance of 50 mmbetween chucks is 50 N/mm² or more.

A tube according to the present invention has a large tensile strength,while having a large tensile elongation at break, and thus it can besuitably used, for example, in a case where a PTFE tube is deformed byextension to be used for coating a core material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a DSC curve of a PTFE tube according to the present invention.

FIG. 2 is a diagram illustrating a relationship between melting energycalculated from an endothermic peak at 370° C.±±5° C. and tube tensilestrength in the PTFE tube of the present invention.

REFERENCE SIGN LIST IN DRAWINGS

-   -   1: Endothermic Peak at 370° C.±5° C.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a PTFE tube according to an embodiment of the presentinvention will be described in detail. The embodiment which will bedescribed below does not limit the inventions relating to the scope ofclaims and all combinations of features described in the embodiment arenot essential for establishing the present invention.

In the embodiment of the present invention, the thickness of a PTFE tubeis 0.1 mm or less. Specifically, the thickness thereof is 0.005 to 0.1mm, preferably 0.01 to 0.08 mm, and further preferably 0.01 to 0.05 mm.Alternatively, a PTFE tube has a thickness of 5% or less of the outerdiameter thereof, and preferably, 4% or less of the outer diameterthereof. When the PTFE tube is used as a part of a layer of a catheter,if the thickness is thin, it is possible to reduce the diameter of thecatheter without disturbing the function of the catheter.

The PTFE tube in the present invention has a tensile elongation at breakof 350% or more. More preferably, the PTFE tube has a tensile elongationat break of 450% or more. The tensile elongation at break means anelongation of a tube until the tube is broken, when being measured at apulling rate of 50 mm/min, under the surrounding environment of 23°C.±2° C.

The PTFE tube in the present invention has a melting energy of 0.6 J/gor more. The melting energy is calculated from an endothermic peak at370° C.±5° C. in a procedure of increasing a temperature in differentialscanning calorimetry (DSC). If the DSC measurement is performed on asample obtained by crushing the PTFE tube in the present invention,endothermic peaks by melting crystals are observed. Due to variety ofcrystal structures, two peaks on a low temperature side and on a hightemperature side are observed.

FIG. 1 illustrates an example of a DSC curve of a tube in an embodimentof the present invention. In a case of the PTFE tube in the presentinvention, in the procedure of increasing a temperature at a temperaturerising rate of 10° C./min, a large endothermic peak is observed in thevicinity of 327° C. and a small endothermic peak is observed in thevicinity of 370° C. The melting energy can be calculated from an area ofthe endothermic peaks. It is considered that the endothermic peak at thevicinity of 327° C. is caused by melting a folded chain crystal and theendothermic peak at the vicinity of 370° C. is caused by melting astretched chain crystal. In a case where extension is performed afterthe tube is formed, the endothermic peak 1 at 370° C.±5° C. tends to belarge. In order to increase the tensile strength of the tube, it iseffective that molecules of a resin forming the tube are arranged in anaxial direction of the tube in which the main chain is stretched.Entangled fibrils are paralleled and arranged in an extrusion flowdirection, that is, the axial direction of the tube, when the fibrilsare discharged from an outlet of a mold. It is considered that thearranged fibrils show an endothermic peak in the vicinity of 370° C., asthe stretched chain crystal. The PTFE tube in the present inventionforms a tube in which the melting energy of the endothermic peak 1 islarge while extension of the tube after formation is suppressed to be 5%or less.

The tube after formation is not extended, and thus a tube having a largetensile elongation at break is obtained. In a case where, for example,the PTFE tube is extended to be used for coating a core material, it isdesirable that the tube has a tensile strength of 50 N/mm² or more whena tube displacement amount when being measured at a distance of 50 mmbetween chucks is 10 mm (hereinafter referred to as “a tube displacementamount”), or the tube has a tensile strength of 70 N/mm² or more whenthe tube displacement amount is 20 mm. When the tube has a meltingenergy of 0.6 J/g or more at 370° C.±5° C., it is possible to obtain atube having a tensile strength f 50 N/mm² or more when the tubedisplacement amount is 10 mm, or a tube having a tensile strength of 70N/mm² or more when the tube displacement amount is 20 mm.

The tensile strength referred in the present invention indicates atensile strength when a tube displacement amount (extended amount) at aninitial time of pulling is 10 mm or 20 mm in a tensile test. In theabove-described method of coating a core wire with a PTFE tube, thetensile strength for a period until the PTFE tube is extended andadheres to the core wire is required. Thus, the tensile strength whenthe displacement amount of the tube is 10 mm or 20 mm is used as acriterion for evaluating the tensile strength for that period.

Hereinafter, a configuration of the PTFE tube in the embodiment of thepresent invention will be described in detail.

There are two types of PTFE powder for forming: fine powder and moldingpowder. In the embodiment of the present invention, fine powder obtainedby emulsion polymerization is used. The fine powder has properties ofdeforming with fibrillation if a shearing force is applied. In pasteextrusion forming, these properties are used. The paste extrusionforming is a method as follows. The fine powder is mixed with an organicsolvent which is generally referred to as an auxiliary agent (lubricant)and the mixture is compressed, thereby creating a preformed body. Thepreformed body is extruded at a forming temperature of 70° C. or lowerby using an extrusion machine, so as to perform formation. The pasteextrusion forming is used for creating a film, a tube, an electric-wirecoating material, and the like.

PTFE used in the embodiment of the present invention may be ahomopolymer of tetrafluoroethylene (hereinafter referred to as “TFE”) ormay be modified PTFE. The modified PTFE is obtained by polymerizing TFEand a small amount of monomers other than TFE. Examples of the smallamount of monomers other than TFE include chlorotrifluoroethylene(CTFE), hexafluoropropylene (HFP), and perfluoroalkyl vinyl ether(PPVE).

It is possible to change heat resistance, abrasion resistance, bendingresistance, and the like of a molded object by using modified PTFE.

The PTFE fine powder is generally powder in which primary particleshaving an average particle diameter of 0.2 to 0.5 μm are aggregated, andthereby secondary particles having an average particle diameter of 400to 700 μm are formed. In the embodiment of the present invention, finepowder having an average secondary particle diameter of 400 to 600 μm isused.

The auxiliary agent is added to PTFE fine powder, and thus allows thePTFE fine powder to be made to be a paste and allows extrusion to beperformed. Thus, an organic solvent having high lubricity is preferablyused as the auxiliary agent used in the embodiment of the presentinvention. After the auxiliary agent is added to the PTFE fine powder, atube is formed in an extrusion machine by using a mold. If the auxiliaryagent is volatilized during the forming, it is difficult to performstable forming, which is not preferable. It is preferable that theauxiliary agent used in the embodiment of the present invention has aninitial boiling point (IBP) of 150° C. or higher. After the tube isformed by using the PTFE fine powder and the auxiliary agent, theauxiliary agent is removed by volatilizing the auxiliary agent beforethe tube is sintered. At this time, the IBP of the auxiliary agent ispreferably 250° C. or lower, so as to enable the auxiliary agent to bereliably removed. A petroleum solvent is particularly preferably used asan organic solvent which has high lubricity and an IBP of 150° C. to250° C.

An auxiliary agent in which a difference between the interfacial tensionof PTFE and the interfacial tension of the auxiliary agent is small isused as the auxiliary agent used in paste extrusion in the related art(see Patent Document 1). However, it is preferable that the auxiliaryagent used in the embodiment of the present invention has an interfacialtension which is more than 18.5 mN/m of the interfacial tension of PTFEby 4 mN/m or more. It is considered that, since the interfacial tensionof the auxiliary agent is high, the auxiliary agent is difficult to movebetween PTFE particles and is easy to stay on the surface of theparticles. In PTFE paste extrusion, when particles slide in the mode ata time of extrusion, the surfaces of the particles are subjected tofibrillating and the fibrils are entangled. Thus, deformation isdifficult and extrusion pressure is increased. At this time, since theauxiliary agent is present between the particles, entanglement of PTFEparticles is suppressed and the increase of the extrusion pressure issuppressed.

In order to set the thickness of the PTFE tube to be 0.1 mm or less orin order to obtain a tube having a thickness of 5% or less of the outerdiameter, forming is performed under conditions of a very narrow flowpassage in which resin in the mold flows and high Reduction Ratio(hereinafter referred to as “RR”). In the condition of high RR, ashearing force generated between the PTFE particle and the inner wall ofthe mold and between the PTFE particles becomes large. If shear stresswhich is rapidly increased is applied to the PTFE particles, most of thePTFE particles are subjected to fibrillating in one lump and theextrusion pressure is increased. The inside of a die is in a turbulentstate and over-shearing occurs. In a tube which has been formed in anover-shearing state, the surface is rough, distortion occurs in thetube, or defects and the like occur. Further, if the extrusion pressureis too high and exceeds a capability range of the extrusion machine,extrusion is not possible.

In the embodiment of the present invention, the auxiliary agent staysbetween the PTFE particles, and thus an effect of reducing a shearingforce between the PTFE particles and between the PTFE particle and theinner wall of the mold is high, and an occurrence in which PTFE is toofast subjected to fibrillating and an increase of the extrusion pressurecan be suppressed. Therefore, it is possible to obtain a tube in whichdefects of which the number is small inside and outside the moldedobject. In addition, a tube having a large tensile strength is obtained,while having a tensile elongation at break of 350% or more. It is morepreferable that tensile elongation at break is 450% or more.

The tube in the embodiment of the present invention may include a filleror other resins. Examples of the filler include carbon, a metal oxidesuch as alumina, a resin filler, and the like. One or plural types ofthe fillers may be mixed in PTFE and the mixture may be used.

A manufacturing method of the tube in the embodiment of the presentinvention will be described below.

(Forming of Preformed Body)

PTFE and an auxiliary agent are mixed in a tumbler or the like. Asdescribed above, an auxiliary agent having an interfacial tension whichis higher than the interfacial tension of PTFE by 4 mN/m or greater isused. The auxiliary agent preferably has an IBP of 150° C. to 250° C.The mixture of the PTFE and the auxiliary agent is pressed and formed,thereby forming a preformed body.

(Extrusion Forming)

The preformed body is set in an extrusion machine, and is formed to havea tube shape by using a mold. Since the tube according to the embodimentof the present invention has a thickness of 0.1 mm or less, a very highshear stress is applied when the preformed body passes through a taperportion of the mold. Here, in the embodiment of the present invention,an auxiliary agent having an interfacial tension which is higher thanthe interfacial tension of PTFE by 4 mN/m or more is used. Thus, theauxiliary agent stays between PTFE particles and lubricity between thePTFE particles and between the PTFE particle and the inner wall of themold is high. Thus, it is possible to suppress an occurrence of rapidfibrillation of PTFE particles. Accordingly, the increase of theextrusion pressure is suppressed.

A temperature of a die for paste extrusion in the related art is knownto be 70° C. or less (for example, see Patent Document 1). However, inthe embodiment of the present invention, the temperature of a die ispreferably set to be 100° C. to 200° C. and more preferably set to be130° C. to 200° C. Since the temperature of the die is set to be high,fibrillation is accelerated on the surface of the PTFE particles and theformed fibril is discharged from the outlet of the mold, in a state ofbeing entangled. Excessively rapid fibrillation of PTFE is suppressedand fibrillation on the surface of PTFE particle and entanglement offibrils are accelerated, and thus the tube after sintering has a largetensile strength while having a tensile elongation at break of 450% ormore. In particularly, the entanglement of fibrils is accelerated, andthus a tube having a large tensile strength at an initial time ofdisplacement.

(Drying Process)

PTFE formed to have a tube shape is heated at a temperature which isequal to or lower than a melting point of PTFE, so as to volatilize theauxiliary agent. When PTFE is sintered in a post-process, it is notpreferable that the auxiliary agent remains. Thus, the auxiliary agentis sufficiently volatilized. Since the auxiliary agent having an IBP of150° C. to 250° C. is used in the tube in the embodiment of the presentinvention, in a drying process, the auxiliary agent can be sufficientlyremoved. In the drying process, an occurrence of a situation in whichtension is applied to the tube and the tube is extended is suppressed.Thus, for example, the balance of the tube between sending and drawingis adjusted. The adjustment is preferably performed such that theextension of the tube is within 5%.

(Sintering of Tube)

Sintering is performed by heating the dried PTFE tube to a temperaturewhich is equal to or higher than the melting point of PTFE. Generally,the tube is heated at substantially 400° C. Since the tube is heated atthe temperature which is equal to or higher than the melting point, PTFEparticles are adhered to each other.

The invention will be more specifically described based on the followingexamples. The following examples are just only examples and the contentsof the present invention are not limited to the following examples.

EXAMPLES

<Tensile Elongation at Break and Tensile Strength>

A tensile test was performed under an environment of 23° C.±2° C. byusing AUTOGRAPH AGS-1 kN X type which is manufactured by ShimadzuCorporation. The tensile test was performed in conditions of a distanceof 50 mm between chucks and a chuck speed of 50 mm/min.

A stress value when a tube set in the chucks was extended in alongitudinal direction by 10 mm and a stress value when the tube isextended in the longitudinal direction by 20 mm were measured as tensilestrengths. The test was performed until the tube was broken, and thetube extension when the tube was broken was set to be a tensileelongation at break.

<Differential Scanning Calorimetry>

The measurement was performed by using DSC3200SA manufactured by NETZSCHJAPAN Corporation, in a manner that a temperature was increased fromroom temperature at a temperature rising rate of 10° C./min. The meltingenergy was calculated from an area obtained by the endothermic peaks of370° C.±5° C. in the obtained endothermic curve of DSC.

Example 1

18 parts by mass of an auxiliary agent (ISOPER H manufactured by ExxonMobil Corporation) with respect to 100 parts by mass of PTFE fine powder(POLYFLON PTFE F-208 manufactured by Daikin Industries, Ltd.) were putinto a container and mixed. Lumps in the mixture were removed by a sieveof #10 and the resultant was put into a preforming machine, and therebya preformed body was produced. As an extrusion forming machine used inextrusion forming of a tube, a machine in which a cylinder diameter was20 mm and a mandrel diameter was 10 mm was used. An inner diameter of adie was set to 0.77 mm, a core pin was set to 0.66 mm, and a temperatureof the die was set to 120° C. The preformed body was put into theextrusion forming machine. Extrusion was performed at a ram speed of 3mm/min, thereby a tube shape was formed. The formed tube was dried andburned by passing through a first drying furnace (set to be 150° C.), asecond drying furnace (set to be 220° C.), and a firing furnace (set tobe 430° C.). When the tube was dried and burned, the speed of a drawingmachine was adjusted so as not to apply an extra tension to the tube.The finished tube was 0.49 mm in inner diameter, 0.566 mm in outerdiameter, and 0.038 mm in thickness. The obtained tube was cut to be 100mm, and a tensile test was performed. Thus, the tensile strength and thetensile elongation at break were measured. Samples were taken from theobtained tubes in accordance with the number or sites of the tubes. Thetaken samples were ground and mixed, thereby obtaining a test piece. TheDSC measurement was performed on the test piece and the melting energywas calculated from a peak area. Table 1 shows results.

Example 2

A tube was produced in a manner similar to that in Example 1 except thatthe temperature of an extrusion die was set to 140° C. The tensile testand the DSC measurement were performed on the tube.

Example 3

A tube was produced in a manner similar to that in Example 1 except thatan auxiliary agent mixed in PTFE fine powder was set to be ISOPER Mmanufactured by Exxon Mobil Corporation. The tensile test and the DSCmeasurement were performed on the tube.

Example 4

A tube was produced in a manner similar to that in Example 3 except thatPTFE640J manufactured by Du Pont-Mitsui Fluorochemicals Co., Ltd wasused as the PTFE fine powder. The tensile test and the DSC measurementwere performed on the tube.

Example 5

PTFE F-201 manufactured by Daikin Industries, Ltd. was used as the PTFEfine powder and ISOPER L manufactured by Exxon Mobil Corporation wasused as the auxiliary agent. A mixing ratio and a mixing method weresimilar to those in Example 1. A tube was produced in a manner similarto that in Example 1 except that a mold in which an inner diameter of adie was 0.72 mm and a core pin was 0.66 mm was used as the extrusionmold. The tensile test and the DSC measurement were performed on thetube.

Example 6

PTFE640J manufactured by Du Pont-Mitsui Fluorochemicals Co., Ltd wasused as the PTFE fine powder and ISOPER G manufactured by Exxon MobilCorporation was used as the auxiliary agent. A mixing ratio and a mixingmethod were similar to those in Example 1. A tube was created in amanner similar to that in Example 1 except that a mold in which an innerdiameter of a die was 2.61 mm and a core pin was 2.40 mm was used as theextrusion mold. The tensile test and the DSC measurement were performedon the tube.

Comparative Example 1

A tube was produced in a manner similar to that in Example 1 except thatthe temperature of the extrusion die was set to 80° C. The tensile testand DSC measurement were performed on the tube.

Comparative Example 2

Extrusion forming was performed in a manner similar to that in Example 1except that ISOPER E manufactured by Exxon Mobil Corporation was used asthe auxiliary agent. Since extrusion pressure was higher than an upperlimit of the extrusion machine (mold), extrusion was suspended.

Table 1 shows results in Examples, Comparative Examples 1 and 2.

TABLE 1 Comparative Comparative Example 1 Example 2 Example 3 Example 4Example 5 Example 6 Example 1 Example 2 Tube inner diameter mm 0.49 0.490.49 0.49 0.475 1.72 0.49 0.49  Tube thickness mm 0.038 0.038 0.0380.038 0.028 0.053 0.038 0.038 Thickness % for outer 6.7 6.7 6.7 6.7 5.42.9 6.7 6.7  diameter Auxiliary agent interfacial mN/m 23 23 25 25 23 2423 21    tension Extrusion die temperature ° C. 120 140 120 120 120 12080 120     Extrusion pressure kN 21.9 23 19.5 22.7 28.1 18.4 17.8 35<   Melting energy at 370° C. ± 5° C. J/g 1.22 0.945 0.699 0.824 1.34 0.7050.19 — Tensile strength when the tube N/mm² 76.6 75.3 70.0 70.4 93.062.0 17.0 — displacement amount is 10 mm Tensile elongation at break %654 544 506 520 460 583 580 —

FIG. 2 illustrates a relationship between the melting energy calculatedfrom endothermic peaks at 370° C.±5° C. and the tensile strengthregarding the PTFE tubes of the examples and the comparative examples inTable 1. If the melting energy is increased, a tendency of the tensilestrength increasing is shown. In a case where, for example, the PTFEtube is extended to be used for coating a core material, it is desirablethat the tensile strength when the tube displacement amount is 10 mm is50 N/mm² or more, or the tensile strength when the tube displacementamount is 20 mm is 70 N/mm² or more. In the example in which the meltingenergy was 0.6 J/g or more, a tube in which the tensile elongation atbreak was 450% or more and the tensile strength when the tubedisplacement amount was 10 mm was 50 N/mm² or more was obtained.Regarding the tube in Comparative Example 1 in which the temperature ofthe die was set to 80° C. and a manufacturing method in the related artwas applied, the tensile elongation at break was 580% or more, that is,large. However, the tensile strength was only 17.8 N/mm². Thus, if, forexample, the PTFE tube was extended to be used for coating a corematerial, a PTFE tube which practically withstood the stress was notobtained.

Comparative Example 3

A preformed body was prepared in a manner similar to that in Example 1except that ISOPER E manufactured by Exxon Mobil Corporation was used asthe auxiliary agent. The tensile test and the DSC measurement wereperformed on the tube. In Comparative Example 2, since extrusionpressure exceeded a usable range of the extrusion machine (mold) whichhad been used, extrusion was suspended. Thus, the shape was changed tobe a shape of a mandrel so as to withstand the extrusion pressure andforming was performed. Extrusion forming was performed in a mannersimilar to that in Example 1 except for the shape of the mandrel.

Comparative Example 4

A preformed body was created in a manner similar to that in Example 1.The preformed body was put into an extrusion forming machine, and a PTFElayer was extruded on an annealed copper wire having an outer diameterof 0.495 mm. The extrusion forming machine in which a cylinder diameterwas 20 mm, a mandrel diameter was 10 mm, an inner diameter of the diewas 0.6 mm, and the temperature of the die was 120° C. had been used. Aram speed was set to be 3 mm/min. The resultant was dried and burned bypassing through a first drying furnace (set to be 150° C.), a seconddrying furnace (set to be 220° C.), and a firing furnace (set to be 430°C.). After burning, the annealed copper wire was extended and thuspulled out from the PTFE layer. Thus, a tube was produced. The finishedtube was 0.49 mm in inner diameter, 0.566 mm in outer diameter, and0.038 mm in thickness. The tensile test and the DSC measurement wereperformed on the obtained tube in a manner similar to those in Example1.

Comparative Example 5

An annealed copper wire having an outer diameter of 0.495 mm was coatedwith an aqueous dispersion (POLYFLON PTFE D-1 manufactured by DaikinIndustries, Ltd.). Then, drying and burning were performed. The aboveprocess repeated until the outer diameter reached 0.566 mm, and therebya PTFE layer was formed. The annealed copper wire was extended and thuspulled out from the PTFE layer. Thus, a tube was produced. The finishedtube was 0.49 mm in inner diameter, 0.566 mm in outer diameter, and0.038 mm in thickness. The tensile test and the DSC measurement wereperformed on the obtained tube in a manner similar to those in Example1.

Table 2 shows results in Comparative Examples 3 to 5.

TABLE 2 Comparative Comparative Comparative Example 3 Example 4 Example5 Tube inner diameter mm 0.49 0.49 0.49 Tube thickness mm 0.038 0.0380.038 Thickness % for 6.7 6.7 6.7 outer diameter Auxiliary agent mN/m 2123 — interfacial tension Extrusion die ° C. 120 120 — temperatureExtrusion pressure kN 56.5 22.8 — Melting energy at J/g 0.29 0.39Detection 370° C. ± 5° C. impossible Tensile strength N/mm² 36.1 41.012.0 when the tube displacement amount is 10 mm Tensile elongation % 370560 480 at break

In Comparative Example 3, the tube in which a difference between theinterfacial tension of the auxiliary agent and the interfacial tensionof PTFE was only 2.5 mN/m and the tensile strength was small wasobtained. It was considered that, since the extrusion pressure wasincreased too high, an over-shearing state occurred and a good moldedobject was not obtained. The tubes in Comparative Examples 4 and 5 aretubes which have been formed by the method in the related art and have athin thickness. The tensile elongation at break was obtained, but asufficient tensile strength was not obtained.

Example 7

PTFE640J manufactured by Du Pont-Mitsui Fluorochemicals Co., Ltd wasused as the PTFE fine powder and ISOPER G manufactured by Exxon MobilCorporation was used as the auxiliary agent. A mixing ratio and a mixingmethod were similar to those in Example 1. A tube which was 1.9 mm ininner diameter, 1.966 mm in outer diameter, and 0.033 mm in thicknesswas produced. The tensile test and the the DSC measurement wereperformed.

Example 8

A tube was produced in a manner similar to that in Example 1 except thatan auxiliary agent mixed in PTFE fine powder was set to be ISOPER Gmanufactured by Exxon Mobil Corporation. Regarding the size of the tube,the inner diameter was set to 2.3 mm, the outer diameter was set to2.356 mm, and the thickness was set to 0.028 mm. The tensile test andthe the DSC measurement were performed.

Table 3 shows results in Examples 7 and 8.

TABLE 3 Example 7 Example 8 Tube inner diameter mm 1.91 2.30 Tubethickness mm 0.033 0.028 Thickness % for 1.7 1.2 outer diameterAuxiliary agent mN/m 24 24 interfacial tension Extrusion die ° C. 120140 temperature Extrusion pressure kN 18 19 Melting energy at J/g 0.640.72 370° C. ± 5° C. Tensile strength N/mm² 56.1 68.0 when the tubedisplacement amount is 10 mm Tensile elongation % 370 470 at break

In Example 7, a tube in which the tensile elongation at break was 350%or more, the melting energy was 0.6 J/g or more, and the tensilestrength when the tube displacement amount was 10 mm was 56. 1 N/mm² wasobtained. In Example 8, a tube in which the tensile elongation at breakwas 450% or more, the melting energy was 0.6 J/g or more, and thetensile strength when the tube displacement amount was 10 mm was 68.0N/mm² was obtained.

INDUSTRIAL APPLICABILITY

According to the present invention, the tube can be particularly appliedto a medical tube such a catheter.

1. A polytetrafluoroethylene tube having a thickness of 0.1 mm or less,a tensile strength at a tube displacement amount of 10 mm when beingmeasured at a distance of 50 mm between chucks is 50 N/mm² or more, anda melting energy of 0.6 J/g or more which is calculated from anendothermic peak at about 370° C.±5° C. in a procedure of increasing atemperature in differential scanning calorimetry (DSC). 2-3. (canceled)4. A polytetrafluoroethylene tube having a thickness of 5% or less of anouter diameter, a tensile strength at a tube displacement amount of 10mm when being measured at a distance of 50 mm between chucks is 50 N/mm²or more, and a melting energy of 0.6 J/g or more which is calculatedfrom an endothermic peak at about 370° C.±5° C. in a procedure ofincreasing a temperature in differential scanning calorimetry (DSC).5-6. (canceled)
 7. The polytetrafluoroethylene tube according to claim1, wherein the tensile strength at the tube displacement amount of 10 mmwhen being measured at the distance of 50 mm between chucks is 70.4N/mm² or more.
 8. (canceled)
 9. The polytetrafluoroethylene tubeaccording to claim 1, wherein the thickness is 0.05 mm or less.
 10. Thepolytetrafluoroethylene tube according to claim 9, wherein a tensileelongation at break is 350% or more.
 11. The polytetrafluoroethylenetube according to claim 4, wherein the thickness is 0.05 mm or less. 12.The polytetrafluoroethylene tube according to claim 11, wherein atensile elongation at break is 350% or more.
 13. Thepolytetrafluoroethylene tube according to claim 9, wherein the tensilestrength at the tube displacement amount of 10 mm when being measured atthe distance of 50 mm between chucks is 70.4 N/mm² or more.
 14. Thepolytetrafluoroethylene tube according to claim 13, wherein a tensileelongation at break is 350% or more.
 15. The polytetrafluoroethylenetube according to claim 4, wherein the tensile strength at the tubedisplacement amount of 10 mm when being measured at the distance of 50mm between chucks is 70.4 N/mm² or more.
 16. The polytetrafluoroethylenetube according to claim 11, wherein the tensile strength at the tubedisplacement amount of 10 mm when being measured at the distance of 50mm between chucks is 70.4 N/mm² or more.
 17. The polytetrafluoroethylenetube according to claim 16, wherein a tensile elongation at break is350% or more.
 18. A polytetrafluoroethylene tube having a thickness of0.1 mm or less, a tensile strength at a tube displacement amount of 10mm when being measured at a distance of 50 mm between chucks is 50 N/mm²or more, and a melting energy of 0.824 J/g or more which is calculatedfrom an endothermic peak at about 370° C.±5° C. in a procedure ofincreasing a temperature in differential scanning calorimetry (DSC). 19.The polytetrafluoroethylene tube according to claim 18, wherein thethickness is 0.05 mm or less.
 20. The polytetrafluoroethylene tubeaccording to claim 19, wherein a tensile elongation at break is 350% ormore.
 21. The polytetrafluoroethylene tube according to claim 18,wherein the tensile strength at the tube displacement amount of 10 mmwhen being measured at the distance of 50 mm between chucks is 70.4N/mm² or more.
 22. The polytetrafluoroethylene tube according to claim19, wherein the tensile strength at the tube displacement amount of 10mm when being measured at the distance of 50 mm between chucks is 70.4N/mm² or more.
 23. The polytetrafluoroethylene tube according to claim22, wherein a tensile elongation at break is 350% or more.